A saponification product of a vinyl ester/ethylenically unsaturated carboxylic acid ester copolymer has been used as a superabsorbent material and applied in a wide range of applications, for example, sanitary products such as disposable diapers and hygiene products and agricultural or horticultural products, due to its high absorbability and water retentivity. On the other hand, it has been used also as a thickening agent or a dispersion stabilizer for various paints and coating agents, due to the function that resin absorbs water to swell.
Patent Literature 1 discloses a process for producing water-insoluble hydrogel having high absorbability, characterized in that a copolymer composed of 20 to 80 mol % of a vinyl ester component and 80 to 20 mol % of an acrylate ester or methacrylate ester component is saponified in the presence of an alkali catalyst and a solvent and under conditions that the copolymer does not dissolve.
Patent Literature 2 discloses a process for producing a superabsorbent resin having an average particle size of 3 to 30 μm, which comprises homogenizing an aqueous dispersion system comprising monomers composed mainly of a vinyl ester and an ethylenically unsaturated carboxylic acid ester, a polymerization catalyst and additionally at least one selected from the group consisting of a dispersant agent and an anionic emulsifying agent, obtaining super fine polymer particles by polymerization, and saponifying them in the presence of an alkali and a dispersion medium.
Patent Literature 3 discloses a process for producing a liquidous absorbent resin by treating a saponification product of a copolymer of a vinyl ester and an ethylenically unsaturated carboxylic acid ester with an oxidation agent such as hydrogen peroxide.